The Nylas CLI is a versatile tool that simplifies the process of testing webhooks without needing an external web server by setting up a webhook tunnel to simulate server notifications triggered by events like email reception or link clicks. This tool enhances application efficiency by eliminating the need for repeated requests, thereby allowing applications to respond swiftly to important events. The process involves creating a temporary webhook tunnel using the Nylas CLI, which can be enhanced with a local PHP web application to receive and display webhook data in a readable format. For broader accessibility, the PHP application can be deployed on Heroku, utilizing SQLite for temporary data storage, although PostgreSQL is recommended for persistent storage in future deployments. The integration of Nylas CLI with PHP and Heroku allows users to track and display webhook events, offering efficient notification handling and decision-making capabilities.